1. Field of the Invention
The present invention relates to a color filter used for a color display such as a liquid crystal display or the like, a color filter forming material and a process for producing the color filter.
2. Description of Related Art
The range of applications of color filters is growing more and more in the field of electrics such as portable information terminals, personal computers, word processors, amusement devices and television devices, as well as display panels used for various electronic devices and electrical devices.
For instance, color filters used for color liquid crystal displays generally have a structure in which pixels of each of red (R), green (G) and blue (B) are formed, and a black matrix is formed in gaps between the pixels with the intention of improving display contrast.
Among color filters like this, those produced by making use of a pigment dispersion method or a dyeing method have been in the majority until now. In the pigment dispersion method, a photoresist in which a pigment is dispersed is applied to a substrate glass, and pattern exposure and a developing step are carried out. This method is superior in pattern edge, resolution and film uniformity. However, this method has a problem that a photoresist step is required, and since a pigment is used, color regulation cannot be accomplished so simply as in the case of using a dye. In addition, this method has the drawback that material loss is increased when a photoresist is applied to a substrate using a spin coating method, and thus coating nonuniformity is large in a case of applying the photoresist to a substrate having a large area. The dyeing method is a method in which a pattern of a transparent resin comprising gelatin or the like provided with light sensitivity is subsequently dyed. This method is characterized by high light transmittance due to transparency of the dye and by easy adjustment of chromaticity due to an abundance of types of dye, but has the drawbacks, for example, that the number of steps, such as a photoresist step, is larger than in the pigment dispersion method.
Further, a printing method, an electrodeposition method and an ink jet method are known as methods of producing a color filter. The printing method is a method in which each color is printed one by one. Thus, it is difficult to align each color pattern, and this method therefore has the drawbacks that the resolution of a pixel is low and film thickness is nonuniform. Therefore, this method involves difficulty when dealing with the formation of a highly accurate image pattern, but it has a high utility factor. The electrodeposition method makes it possible to obtain a color filter which has a relatively high resolution and less nonuniformity of a color layer, but this method has difficult points in that the production steps are complicated and solution control is difficult. The ink jet method has problems concerning resolution and color mixing among pixels adjacent to each other.
Also, in a method of production of a color filter according to the above methods, measures are taken in which a separate color pattern is formed of each color and these plural color patterns are overlapped on each other with these patterns being aligned to each other. In this method, accurate alignment is required. Also, pixels may overlap each other and parts where light is leaked may occur. When pixels are overlapped on each other, the resulting color filter film is made nonuniform and irregularities (projections) are formed on the surface of the film, giving rise to problems such as color mixing, color misregistration, nonuniformity, light leakage and scattering. These problems are particularly significant when manufacturing a black matrix.
Moreover, in recent years, attempts have been made to use a plastic substrate in place of glass as the substrate of a color filter, to satisfy demands for preventing breakage of the substrate and for developing a lighter and thinner type of liquid crystal display. However, in the case of using a plastic substrate, it is difficult to keep a perfectly flat surface, which poses a problem that it is difficult to sequentially incorporate structural components on the substrate compactly.
Hence, conventional methods for producing a color filter as described above have complicated production processes, require large investments in plant and equipment and give rise to problems of waste materials and waste liquid, which make burdens of cost and time heavy. Further, it is expected that demand for reflection-type and semitransparent-type liquid crystal displays such as plastic cells will grow in the future. As a method of producing high quality color filters which can be used in such applications, it is desired to develop a method for production of a color filter having high productivity in terms of low material loss, simplicity and the like, and having low cost and environmental load.
However, a method of producing a color filter which satisfies all of these requirements has not been achieved so far.
It is an object of the present invention to provide a color filter having high resolution and flatness, a color filter forming material which can form such a color filter and a process for producing a color filter, the process enabling production of the color filter by using a method which has high productivity and is decreased in cost and environmental load.
This object of the present invention can be attained by providing the following color filter, color filter forming material and process for producing a color filter.
The present invention provides a color filter including a light-transmissive support and at least two color-developing layers that develop hues different from each other, the color-developing layers having been laminated on the support and each color-developing layer having been developed in a predetermined color pattern, and respective developed color patterns of the layers including a region at which the color patterns overlap in a direction of lamination, which region has a hue expressed by subtractive color mixing of the colors of the layers that are developed at the region.
Also, the present invention provides a color filter including a light transmissive support and two or more color-developing layers developing hues differing from each other, the color-developing layers being laminated on the support and each color-developing layer being developed into a specific color pattern, wherein the developed color pattern of each layer is not overlapped in the direction of lamination.
These color filters are each constituted of a continuous layer and therefore have excellent characteristics that they have a surface free from irregularities or projections and exhibiting high flatness, and also there is no deficient portion to cause light leakage in the color-developing layer. Also, the latter color filter has an excellent characteristic that high color purity is obtained irrespective of a direction of view, which is not found in conventional color filters.
Further, the present invention provides a color filter forming material including a light-transmissive support and at least two photosensitive and heat-sensitive color-developing layers capable of developing hues different from each other, the color-developing layers being laminated on the support.
In addition, the present invention provides a process for producing a color filter from the color filter forming material that includes at least two photosensitive and heat-sensitive color-developing layers, which are capable of developing hues different from each other, laminated on a light-transmissive support, the process including the steps of: forming latent images by exposing each of the photosensitive and heat-sensitive color-developing layers, such that at least two latent image-formed regions overlap each other in a direction of lamination; developing color by heating the photosensitive and heat-sensitive color-developing layers; and fixing color-developed patterns formed by the step of developing color.
Moreover, the present invention provides producing a color filter from the color filter forming material that includes at least two photosensitive and heat-sensitive color-developing layers, which are capable of developing hues different from each other, laminated on a light-transmissive support, the process including the steps of: forming latent images by exposing each of the photosensitive and heat-sensitive color-developing layers, such that latent image forming regions of the respective layers substantially do not overlap each other in a direction of lamination; developing color by heating the photosensitive and heat-sensitive color-developing layers; and fixing color-developed patterns formed by the step of developing color.
The process for producing a color filter according to the present invention ensures that a color filter having such excellent characteristics as mentioned above can be produced simply by performing only the steps of exposing, heating and fixing the color filter forming material and so a photolithographic step which is conventionally required is unneeded, improving productivity, whereby the production cost of the color filter can be significantly decreased. Also, because all the steps are carried out in a dry condition, environmental load can be decreased.